1. Technical Field
The present invention relates to a method and device for synthesizing a radioactive methyl iodine (CH3131I) tracer, and more particularly to a method and device for synthesizing a radioactive methyl iodine tracer suitable for use in evaluating the ability of impregnated activated carbon to adsorb radioactive organic iodine according to ASTM D 3803 (Standard Test Method for Nuclear-Grade Activated Carbon).
2. Description of the Related Art
Performance of impregnated activated carbon used in nuclear power plants must be strictly tested. In order to evaluate the ability of impregnated activated carbon to remove radioactive organic iodine, a radioactive methyl iodine (CH3131I) tracer is utilized under high humidity and atmospheric conditions.
Conventionally, radioactive methyl iodine is synthesized using a device of FIG. 1 by subjecting an anhydrous methanol solution and a concentrated sulfuric acid (c-H2SO4) solution to mixing, stirring and cooling, adding sodium iodide powder (6.0 g when using 5.2 ml of the anhydrous methanol solution and 1.2 ml of the concentrated sulfuric acid solution) with stirring, performing refluxing at 40° C. and heat distillation, thus separating a secondary reaction product, adding a 5% sodium thiosulfate (Na2S2O3) aqueous solution to the secondary reaction product thus isolating methyl iodine, separating the sodium thiosulfate solution layer from the secondary reaction product, and performing washing using distilled water, thereby preparing a radioactive methyl iodine solution at a yield of about 40%. Specifically, the total five steps are applied.
Step 1: Synthesis of methyl iodine (10° C., 30 min)2CH3OH+H2SO4→(CH3O)2SO2+2H2O, (CH3O)2SO2+2Na127I→2CH3127I+Na2SO4  (1)
Step 2: Substitution of methyl iodine and radioactive iodine (40° C., 30 min)2CH3127I+2Na131ICH3127I+CH3131I+Na127I+Na131I  (2)
Step 3: distillation of methyl iodine (60° C., 7 hours)CH3OH+CH3127I+CH3131I+2H2O+127I2+(Na127I+Na131I+Na2SO4)↓→CH3OH+CH3127I+CH3131I+2H2O+127I2  (3)
Step 4: Removal of iodine (30° C., 5 min)CH3127I+CH3131I+CH3OH+H2O+(127I2+Na2S2O3)↓→CH3127I+CH3131I+CH3OH+H2O  (4)
Step 5: Removal of methyl alcohol and aqua (30° C., 5 min)CH3127I+CH3131I+CH3OH+(H2O+CaCl2)↓→CH3127I+CH3131I  (5)
Briefly, the conventional mechanism for synthesizing a radioactive iodine (CH3131I) tracer includes substituting the (CH3O)2SO2 intermediate compound in an aqueous solution state with 131I in the steps 1 and 2, thus synthesizing CH3131I.
Because the tracer thus synthesized is present together with a variety of reagents, it is distilled so that volatile H2O, CH3OH, CH3127I, and CH3131I are distilled from various mixtures, after which only CH3127, 131I should be purified. As such, only the step 3 including reflux and distillation requires 7 hours or longer, and after completion of the final step 5, about 1 ml of radioactive iodine tracer (CH3131I) may be obtained.
The conventional method of preparing a radioactive methyl iodine tracer is problematic because the radioactive material sodium iodide (Na131I) should be handled for a considerable period of time (about 10 hours), and thus workers may be increasingly subjected to external exposure from radioactive sodium iodide due to leakage of the volatile material during the distillation and to internal and external exposure from radioactive methyl iodine (CH3131I).
Furthermore, the conventional method is very complicated because of using radioactive materials such as sodium iodide (Na131I), and chemicals such as anhydrous methyl alcohol, concentrated sulfuric acid, sodium thiosulfate, calcium chloride, etc., with the use of a water bath, a low-temperature cooler, a distiller, etc.